It is often desirable to secure eyewear to a wearer's head to avoid loss or movement of the eyewear. For eyewear (e.g. goggles or mask) which is worn in sporting activities such as swimming or skiing, it is especially important to secure the eyewear to the wearer's face and elastic head straps are typically used for this purpose.
Ideally these head straps need to be adjustable to cater for a range of head sizes and to allow the wearer to select their desired strap tension. One way of achieving this adjustability has been to provide a buckle through which the strap passes, the free end of the strap being pulled to tighten the head strap once the eyewear is in place. One problem with this adjustment arrangement is that the free end can cause discomfort and distraction by flapping around when the eyewear is in place.
Another problem with the known adjustment arrangements is that the buckle can protrude significantly from the back of the head when the eyewear is being worn. This can cause discomfort, especially if a tight fitting hat or cap is worn over the top of the strap. Furthermore, in the case of swimming goggles, the protrusion of the buckle can create frictional drag (whether or not the buckle is covered by a swimming cap) and this is undesirable.
Finally, once the strap is tightened, it can be difficult to readjust the tension in the strap for several reasons. Firstly, it is more difficult to loosen the head strap than it is to tighten it and it may be necessary to remove the eyewear in order to loosen the head strap. Secondly, if the wearer is participating in competitive sporting activities, it may only become apparent that the head strap is incorrectly adjusted once the competitive activity has commenced, by which time it will be too late to make any further adjustments. For this reason, it is desirable to provide some means for allowing a reliable and accurate measurement of tension within the head strap so that the wearer can ensure that the head strap is correctly adjusted.